System and method for operating electric furnaces



May 18 1926; 1,584,763

R. J. GAUDY SYSTEM AND METHOD FOR OPERATING ELECTRIC FURNACES Filed July 51, 1918 J? Jan L5 Gamay MGM Patented May 18, 1926.

PATENT FFIC'E.

RALPH JARVIS GAUDY, OF CHICAGO, ILLINOIS, ASSIGNOR OF ONE-HALF TO EDSON O. SESSIONS, OF CHICAGO, ILLINOIS.

SYSTEM AND METHOD FOR OPERATING ELECTRIC FURNACES.

Application filed July 31,

My invention relates to an improved sys tem and method for operating electric furnaces by which the time intervals required to effect the melting ofthe metal in the furi nace is materially reduced, and by which a considerable amount of electrical energy is saved in the operating of the furnace during the melting interval.

As is wellknown in the art theelectric.

' furnace is frequently employed to melt and refine iron to form steel therefrom, and in carrying out this operation the material placed in the furnace for treatment is frequently scrap iron. Electrodes are provided for engagement with the material in the furnace, such as the scrap iron referred to, to cause current to flow from suitable electric supply circuits through the material in the furnace, which current flow through said material first serves to heat the material to the melting point, and when subsequently continued the current flow effects a purifica tion for the melted metal. ployed in connection with the electrodes re ferred to, which, under the action of the current flowing through the electrodes, move or permit the electrodes to be moved into engagement with the material in the furnace when they are not in contact therewith, and to withdraw the electrodes somewhat from the material in the furnace when the cur rent flow through the electrodes becomes too great to properly effect the melting and refining operations. On account of the relative slnggishness of the regulating devices in responding to variations in the current 7 flow through the electrodes it frequently occurs, particularly during the melting portion of the treatment that there are .considerable intervals of time relatively to the operating intervals, when there is no current flow at all through the electrodesand for this reason it requires a considerable time interval to heat the solid material in the furnace sufficiently to melt it. consists in providing a means for maintaiir ing a flow of current through the electrodes and the metal or material being heated during practically the entire heating period, and

at the same time preventing a large part of the fluctuation of the current flow through the electrodes during this interval. More specifically my invention consists in impressing or superposing. upon the conducting paths through the electrodes and metal or Devices are em- My invention 1918. Serial No. 247,494.

material being heated electro-motive force of high voltage and preferably high frequency provided by any suitable generating means, whereby I maintain at all time conductive arcs between the ends of the electrodes and the metal or material being heated, which afford relatively good conductive paths for the main current flowing between the electrodes and the said metal or material, and as a result the relatively large cur rent flow through the electrodes, supplied by the main conductors, heats the metal or material and is maintained with but slight variation in its volume, Whereas without the use of means for maintaining said current flow,

since the electro-motive' force of the main in an electric furnace, which electro-motive force is preferably of high frequency and superposed upon the lower electro-motive force of relatively low frequency employed I in connection with the current supplied by the main conductors for heating the metal -or material in the furnace. My invention does not require any change in the construction of the furnace or the means employed to supply the main current-flow to the metal or material in the furnace, nor does it .require any change in the regulating devices used to control the position of the electrodes, but on the other hand, the devices employed for carrying out my system and method of operation inay be readily attached to electric furnaces already in operation.

By my invention I also provide a protective means for preventing the high voltage, high frequency currents employed from doing possible damage or injury to the electrical equipment employed to supply the, main current to the electrodes for heating andmelting the metal or material in the furnace.

My invention will best be understood by reference to the accompanying drawings showing a preferred embodiment of means that may be employed for carrying out said invention, in which, 9

Fig. 1 shows diagraiuniatically an electric furnace and circuit connections for supplying the main current to the electrodes and for also supplying the high tension, high frequency current thereto,

Figs. 2, 3, and 4 are detail diagrammatic views of the relation of one of the electrodes to the metal or material being treated at different times during the heating operation,

Fig. 5 is a diagramn'iatical view of a wave of current illustrating the operation of one of the electrodes under conditions heretofore employed, and,

Fig. 6 illustrates in a view similar to Fig. 5 the current flow through one of the electrodes by using my invention.

Similar nume'als refer to similar parts throughout the several views. i

As shown in Fig. 1 an electric furnace is indicated diagran'imatically as consisting of a casing 10 of metal lined with refractory material 11 such as fire clay, in which a. cavity is formed to receive the metal or material 12 to be treated, which in this case may be assumed to be scrap iron. Electrodes 13, J4 and 15, preferably of carbon,are disposed vertically above the material 12 with their lower ends resting upon said material, the upper ends of the electrodes are engaged by -metal rods 16, 17 .and 18 respectively and these rods in turn are engaged by clutches 19, 20 and 21 respectively. These clutches which are shown diagrammatically as one form of mechanism that may be employed to regulate the electrodes are similar in construction, as a result of which it is necessary to describe but one of them, as for example the clutch 19. This clutch is loosely engaged at its outer end by the lower end of a core 22 and also be a spring 23 tending to move the clutch downward so that its right hand end rests against a fixed abutment 24. \Vhen the core 22 is raisedthe clutch 19 engages'the rod 16 to lift it and also the electrode 13 connected therewith until the clutch engages a second abutment 25, disposed at a distance from the abutment 24, permitting suflicient motion of the electrode 13 to decrease the current flow from the electrode 13 to the lowest desired amount. Vhen the core 22 is permitted to drop under the action of the spring 23, the clutch 19 engages the lower abutment 24, which frees the clutch from the rod 16, thus permitting the electrode 13 to drop into engagement with the material 12.

The electrodes 13, 14 and 15 are connected respectively by flexible conductors with one terminal of the solenoids 26, 27 and 28, the other terminals of which are connected with the main supply conductors 29, 30 and 31. The solenoid 26is operatively related to the core 22 and the solenoids 27 and 28 are similarly related in a manner not shown, to the clutches 20 and 21 respectively. The main conductor 29 is connected to one terminal of the secondary windings 32 and 33 of the transformers 35 and 36. The main conductor 30' is connected with the other terminal of the secondary winding 33 andwith one terminal of the secondary winding 34 of the transformers 36 and 37 respectively. The main conductor 31 is connected with the other terminals of the secondary windings 32and 34, thus connecting the secondary windings 32, 33 and 34 in a three phase delta arrangen'ient. The transformers 35, 36 and 37 are provided with primary windings 38, 39 and 40 respectively. The primary winding 38 has one of its terminals connected with one terminal of the primary winding 40, and to one terminal of the regulating resistance 41 by wire 42. The other terminal of the primary winding 38 is connected with one terminal of the primary winding 39 and by wire 43 with one terminal ofthe regulating resistance 44. The other terminals of the primary windings 39 and 40are connected together and by wire 45 to one terminal of the regulating resistance 46. Contact arms 47, 48 and 49 are provided for engaging the regulating resistance 41, 44 and 46 respectively, these arms being insulated from each other and connected through flexible conductors with wires 50, 51 and 52 extending to a three phase generator employed to supply the main current to the furnace. It will be understood that any desired form of current regulating devices maybe employed for the purpose of controlling the current flow through the several electrodes.

The trans'fiirmers 35, 36 and'37 are shown diagrammatically as located in a transformer tank 54. preferably of metal and may be immersed in oil in said tank as is common practice in the art.

The apparatus thus far described is dia grammatically substantially the same as heretofore used in connection with electrical furnace practice. In using this construction without the improved meansconstituting my invention, the current flow from the generator 53 through the primary windings 38, 39 and 40 is regulated by contact arms 47, 48 and ,49, so that the low tension. high volume current delivered by the secondary windings 32, 33 and 34 will flow through the solenoids 26, 27 and 28, the electrodes 13, 14 and 15 and the material 12. At the beginning of this operation the material 12 is cold and a relatively large current flow is required toheatthe material and bring it to the melting point. During the heating operation the condition indicated diagrammatically' in Figs. 2, 3 and 4 for the electrode 13 repeatedly occurs. As indicated in Fig.2 the electrode rests on a projecting point of the material, which in case of scrap iron isa' good conductor thus permitting momentarily a large current flow through the electrode. This current flow acting'"upon the solenoid 26 actuates the clutch 19 and tends to raise the electrode. At practically the same time, however, on account of the relatively small cross-section of the conducting point with which the electrode is in engagement the projecting point is melted and drops away from the electrode, thus opening the circuit and leaving a gap as indicated at 55 in Fig. 3, which gap is too large to be arced over by the relatively low potential of the current flowing through the conductor 29. As a result current flow through the conductor 29 and the solenoid 26 is interrupted, the core 22 drops under the action of the spring 23 and the electrode 13 drops'into engagement with the material 12 as indicated in Fig. 4. Before this occurs, however, an appreciable time interval elapses as a result of its first being. necessary for the clutch 19 to become disengaged and of it then being necessary for gravity to overcome the inertia of the electrode 13 and the parts connected therewith. This operation recurs repeatedly at each electrode during the heating operation and while the metal or material is being sufliciently melted to afford the electrode a good conducting path to the metal or material, and as the effective, or heating portions of this interval are but momentary and the portions during which the electrodes are being brought again into engagement with the metal or material are appreciable and relatively considerable in length, the heating current is in fact flowing through the electrodes but a small part of the time and the time required to heat the metal or material to a condition of anything likeuniform operation is long. During this interval the apparatus supplying the main conductors with current must, of course, bein constant operation andthelosses incident to the op eration of this part of the system are constant, and furthermore on account of the current flow being but momentary a larger current is employed to secure the heating effect than would otherwise be required. There are therefore material losses from two causes, first from the inactive condition of the furnace during a major portion of the heating interval, which results in materially reducing the capacity of the furnace, and second from the electrical losses of the system during the inoperative periods.

The efi'ect'of the operation thus far described is shown diagrammatically in Fig. 5

representing the current flow through one of the electrodes, as for example the elec trode 13. The current wave shown is-of approximately sine form and for purposes of illustration it may be assumed that the wave 56 occurs for the condition of theelectrode shown in Fig. 2, and that the nature of the come in contact with the material in the fur:

nace, which for the current wave shown in Fig. 5 may be assumed to be seven single waves, after which for the condition indicated in Fig. 4 a wave of current 57 flows from the electrode to the material 12, and assuming that the projections of the material are still sufliciently small to be instantly melted by the current flow, the current may be assumed to flow for but this single wave, and a succession of dotted waves follows indicating an inoperative interval after which current may flow as indicated by the wave 58 for another single wave length. In other words, the single waves shown in full lines at 56, 57 and 58 represent the operative portions of this part of the heating interval or period, and the dotted wavesindicate the inoperative portions and afford a diagrammatic indication of the inefliciency of the system of operation described.

To carry out my invention I provide an additional alternating current generator 59 connected through a switch 60 with the primary Winding 61 of a transformer 62. The transformer 62 is provided with high tension secondary windings 63, 64 and 65. The secondary winding 63 has one of its terminals connected through a condenser'66 by Wire 67 and a flexible conductor with the electrode 13. The other terminal of this winding is connected by wire 68 through the re actance coil 69 with a terminal 70, which may be a metal rod embedded in the material 12. The secondary winding 64 is similarly connected through the condenser 71 and reactance coil 72 by Wires 7 3 and 74 with the electrode 14 and the terminal rod 75. The secondary winding is similarly connected through the condenser 76 and the reactancq coil 77 by wires 78, and 79 with the electrode 15 and the terminal rod 80. The rods 70, 75 and 80 are preferably disposed in the material 12 near the electrodes 13, 14 and 15 respectively. The electro-motive force developed by each of the secondary windings 63, 64 and65 is very high, as for example 100,000 volts, as a result of which this voltage causes a discharge from the electrodes to the material 12 across air gaps that could not be bridged by the low Volta e on the main conductors 29, 30 and 31. T e operation of each secondary winding is substanthe relation indicated in Fig. 2 and the resulting current flow may operate substantially as above described producing the condition indicated in Fig. 3. The gap is preferably controlled by the regular mechanism so that it may readily be bridged by the high tension electro-motive force delivered from the winding 63, as a result of which a discharge is produced across the gap 55 by the high tension electro-motive force, which breaks down the gap and affords a path for the low tension current to follow. As a result the current flow is not entirely interrupted as in the case above described and there is not the same abrupt tendency of the regulating devices of the electrode to move the electrode into engagement with the material. On the other hand the main current flow being somewhat small owing to the re a tively large gap the regulating devices move the electrode somewhat nearer the material 12 for which condition the main current increases sulticiently to prevent further downward movement of the electrode and a sub stantially stable condition results. \Vhen through the wearing away of the electrode the clutch 19 is entirely released, although at this time a relatively small heating current may be flowing, the electrode 13 begins to move towards the n'laterial 12, which results in an immediate increase in the current flowing and a sutlicient increase in the euergization of the solenoid 2G to again move the clutch 19 into engagement. As a result the gap 55 for this condition is not closed at all and an abnormal current flow is prevented, thus preventing extreme operation of the regulating devices. On theother hand if the gap between the electrode 13 and the material 12 is too large to be bridged over by t the high tension electro-motive force when the clutch 19 is released or when the electrode 13 begins its movement towards the material- 12, the gap is spanned by high tension discharge before the electrode engages the material 1:2 and a path is at once established for the current flow from the main conductor 29, thus in any event preventing an abnormal rush of current, which would produce extreme operation of the regulating devices.

The effect of the high frequency current referred to is much increased by the use of the condensers 66, 71 and 76, since these 0011- densers serve to produce a high frequency oscillatory discharge between the electrodes and the terminal rods with the result that the high potential impressed by the secon dary windings 63, 4 and is available at any instance to cause current flow from the electrodes 13, 14 and 15 to the-corresponding terminal rods through the material 12, thus affording a path for the flow of current from the conductors 29, 30 and 31 at all times to and through the material 12.,

The relation of the current flowing from the transformer 62 and from the conductors 29, 30 and 31 is indicated diagrammatically in Fig. 6 for one of the electrodes, as for example the electrode 13, the wave 81 being the current wave resulting from the high frequency discharge produced by the high tension electro-motive force'wave 82 delivered by the winding 63 and condenser 66 and the wave 83 representing the practically continuous current wave delivered from the conductor 29 under these conditions. From the above it will be seen that by my invention I cause each electro-motive force wave delivered from the secondary windings 32, 33 and 3st to be cilective in'sending current through the electrodes 13, 14 and 15 and the material 12 and thus materially reduce the time interval required to heat the material 12 to its melting point, and furthermore since the heating operation is continuous the quantity of current flowing through the conductors 29, 30 and 31 during the heating interval may be materially reduced without in any way decreasing the etliciency ofoperation.

To provide against; the possibility of the high tension elcctro-motive force delivered by the secondary windings of the transformer (32 damaging the transformers 35, 36 and 37 I provide protective devices as follows:

The wire (38 is connected by wire 84: through a spark gap 85 with the main eonductor 29, the wire H is connected by wire 86 through a spark gap 87 with the main conductor 30, and the wire 79 is connected by wire 88 through a spark gap 89 with the main conductor 31. The spark gaps 85, 87 and 89 are-adjusted so that the dielectric value of each is somewhat less than the di- 1 electric strength of the insulation of the transformer windings 35, 36 and 37 and of the insulation of these windings from the tank 54, and that the spark gaps have a sufficiently high dielectric value to cause the high tension electro-motive force to bridge the gaps between the electrodes 13, 14 and 15 in the manner above described. As a result of this construction, if pcrchancc there should be a grounded connection indicated by the dotted line 90 between the tank 54 and the casing 10, the high tension electromotive force will not discharge from the secondary windings 32, 33 and 3 1 to the tank and thus through the grounded connection to the furnace, but will take the lower resistance paths through the spark gaps 85, 87 and 89 and thus protect the transformers 35, 36 and 37 from dan'lage.

It will be understood that I do not limit myself to any particular construction of electric furnace in carrying out my invention, nor do I limit myself to the heating or treatin g of any particular material in the furnace, as my invention is applicable to any furnace of the general type described and to the treatment of any material that is subject lit) 50 trode and said material,

to be broken down or melted by current flow.

Nor do I limit myself in carrying out my invention to the particular construction diagrammatically indicated as I may employ any equivalents thereof known to the art at the time of the filing of this application Without departing from the. scope of the appended claims.

WVhat I claim is:

1. In a system for operating electric furnaces, the combination of a receptacle for material to be heated, an electrode, means for causing a main electric current flow through said electrode and material to heat the latter, means for impressing upon said electrode and material a high tension electromotive force, and protective means for preventing discharge from said high tension electromotive force from the windings of the 0 source of said main current.

2. In a system for operating electric furnaces, the combination of a receptacle for material to be heated, an electrode, means for causing a main electric current flow through said electrode and material to heat the latter, means for impressing upon said electrode and material a high tension high frequency electromotive force, and protective means for preventing discharge from said high tension electromotive force from the windings of the source of said main current.

3. In a system for operating electric furnaces, the combination of a receptacle for material to be heated, an electrode, means for causing a main electric current flow through said electrodeand material to heat the latter, means for producing a high fre-' quency electric discharge between said electrode and said material, and protective 40 means for preventing discharge from said high frequency current from the windings of the source of said main current.

4. In a system for operating electric furnaces, the combination of a receptacle for 5 material to be heated, an electrode, means for causing a main low voltage electric current flow through said electrode and material to heat the latter, means for producing a high voltage discharge between said elecand protective means for preventing discharge from said high voltage from the windings of the source of said main current.

5. In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors con nected with said electrodes for causing low tension current flow between said electrodes through said material, and means for producing a high frequencyelectric discharge between each electrode and said material independently of the other electrodes.

6. In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow between said electrodes through said material, and means for producing a. high voltage electric discharge between each electrode and said material independently of the other electrodes.

In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current. flow between said electrodes through said material, and means for producing a high frequencyhigh voltage electric discharge between each electrode and said material independently of the other electrodes. I

8. In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow bet-ween said electrodes through said material, and means for producing a continuous high frequency electric discharge between each electrode and said material independently of the other electrodes.

9. In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow between said electrodes through said material, and means for pro ducing a continuous high voltage electric discharge between each electrode and said material independently of the other electrodes.

10. In a system for operating electric furnaces, the combination of a receptacle for material 'to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow between said electrodes through said material, and means for producing a continuous high frequency high voltage electric discharge between each electrode and said material independently of the other electrodes.

11. In a system for operating electric furnaces, the combination of a. receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow between said electrodes through said material, means for producing a high frequency electric discharge between each electrode and said material independ ently of the other electrodes, and protective means for preventing discharge from said high frequency current through the source of said polyphase current.

' 12. In a system for operating electric furnaces, the combination of a receptacle for materialto be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current-flow between said electrodes through said material, means for producing a high voltage electric discharge between each electrode and said material independently of the other electrodes, and protective means for preventing discharge from said high voltage current through the source of said polyphase current.

13. In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with said electrodes for causing low tension current flow between said electrodes through said material, means for producing a high frequency high voltage electric discharge between each electrode and said material independently of the other electrodes, and protective means for preventing discharge from said high frequency current through the source of said polyphase current. 1

14:- In a system for operating electric furnaces, the combination of a receptacle for material to be heated, an electrode, means for causing a main electric current flow through said electrode and material to heat the latter, a step-up transformer having a high tension secondary winding, conductors extending from said windingtosaid electrodesand said material, a condenser connected with said conductors, and a protective circuit between said conductors and the main current circuit comprising a conductor having a spark gap therein.

15. 'In a system for operating electric furnaces, the combination of a receptacle for material to be treated, a plurality'of electrodes, polyphase electric conductors conneeted with said electrodes for causing low tension current flow between said electrodes through said material, transformingdevices comprising primary and high tension secondary windings, electrical connections between each secondary winding and each electrode and said material, said connections for each secondary winding and electrode being independent of the similar connections between the other secondary windings and the other electrodes, and a condenser conneeted with the connections extending from each secondary windin 16. In a system for operating electric fur,- naces, the combination of a receptacle for material to be treated, a plurality of electrodes, polyphase electric conductors connected with'said electrodes for causing low tension current fiow'between said electrodes through said material, transforming devices .comprising primary and high tension secondary windings, electrical connections between each secondary Winding and each electrode and said material, said connections for each secondary winding and electrode being independent of the similar connections between the other secondary windings and the other electrodes, a condenser connected with the connections extending from each secondary winding, and a protective circuit for each secondary winding between the connections. extending therefrom and the corresponding polyphase conductor, each protective circuit comprising a conductor having a spark gap therein.

17. The method of securing a continuous heating current flow from an electrode to and through a furnace charge consisting in moving said electrode towards and from the charge by automatic means, impressing a relatively low voltage heating current on said electrode and charge and in superposing on said low voltage current between said electrode and charge a high voltage bridging current of sufiicient tension to bridge gaps between said electrode and charge due to automatic adjustment of said electrode too great to be bridged by said low voltage.

18. The method of securing a continuous heating current flow from an electrode to and through a furnace charge consisting in moving said electrode towards and from the charge by automatic means, impressing a relatively low Voltage heating current on said electrode and charge and insuperposing on said low voltage current between said electrode and charge a high voltage bridging current of high frequency and of sufficient tension to bridge gaps between said electrode and charge due to automatic adjustment of said electrode too great to be bridged by said low voltage.

19. The method of securing continuous heating current flow from furnace electrodes to and through a furnace charge consisting in moving said electrodes towards and from the charge by automatic means, impressing on said electrodes and charge a relatively low voltage polyphase heating current and in superposing on said low voltage current between said electrodes and charge a high voltage bridging current of sulficient tension to bridge gaps between said electrodes and charge too great to be bridged by said low voltage.

20. The method of securing continuous heating current flow from furnace electrodes to and through a furnace charge consisting in moving said electrodes towards and from the charge by automatic means, impressing on said electrodes and charge a relatively low voltage polyphase heating current and in superposing on said low voltage current between said electrodes and charge a high voltage bridging current of high frequency and of suflicient tension to bridge gaps beiso tween said electrodes and charge too great to be bridged by said low voltage.

21. In combination, a furnace for receiva charge to be heated, an electrode, means for moving said electrode relatively to said charge tending to maintain .a desired relation between said electrode and charge, means for producing a heating current flow between said electrode and charge, and means for superposing on said heating current a high voltage current of suflicient tension to bridge gaps between said electrode and charge resulting from operation of said moving means too great to be bridged by the Voltage of said heating current.

22. In combination, a furnace for receiving a charge to be heated, an electrode, means for moving said electrode relatively to said charge tending to maintain a desired relation between said electrode and charge, means for producing a heating current flow between said electrode and charge, and means for superposing on said heating current a high frequency high voltage current of sufficient tension to bridge gaps between said electrode and charge resulting from operation of said-moving means too great to be bridged by the voltage of said heating current.

23. In combination, a furnace for receiving a charge to be heated, a plurality of electrodes, means for moving said electrodes relatively to said charge tending to maintain desired relations between said electrodes and charge, means for producing a polyphase heating current flow between said electrodes and charge, and means for superposing on said heating current a high voltage current of suflicient tension to bridge gaps between said electrodes and charge resulting from operation of said moving means too great to be bridged by the voltage of said heating current.

24. In combination, a furnace for receiving a charge to be heated, a plurality of electrodes, means for moving said electrodes relatively to said charge tending to maintain desired relations between said electrodes and charge, means for producing a polyphase heating current flow between said electrodes and charge, and means for superposing on said heating current a high frequency high voltage current of suflicient tension to bridge gaps between said electrodes and charge resulting from operation of said moving means too great to be bridged by the voltage of said heating current.

25. The method of operating electric furnaces consisting in producing a polyphase heating current flow between the furnace electrodes and a charge to be heated and in superposing on said heating current between said electrodes and charge a high ten sion bridging current of negligible heating effect.

26. The method of operating electric furnaces consisting in producing a polyphase heating current flow between the furnace electrodes and a charge to be heated and in superposing on said heating current between said electrodes and charge a high frequency high tension bridging current of negligible heating effect.

In witness whereof, I hereunto subscribe my name this 3rd day of June, A. D. 1918.

R. JARVIS GAUDY. 

